In recent years, a thin film which uses silver or aluminum as a reflector has been used as a lamp reflector for a backlight of a liquid crystal display, as well as a reflection umbrella for the fluorescent lamp and the like. Such a reflector is a reflective board having a structure of a silver or aluminum thin film layer/an adhesive layer/an aluminum plate or a so-called reflective sheet having a structure of a silver or aluminum thin film layer/a white coating/an adhesive layer/an aluminum deposition layer/a polymer film/a white coating, which has been reported, for example, in Japanese Patent No. 2503160, JP1995-32537A, JP2002-116313A, JP2000-221311A and the like.
In recent years, with high pixel number of a liquid crystal display, enhancement of luminance for a backlight has been in demand. Here, as a method for increasing a luminance for a backlight, use of a reflector with a high reflectance capable of entirely using light from a light source can be cited. At present, although a reflector using a silver thin film layer has been properly used, a reflector having much higher reflectance has been demanded from the market.
Although silver has a high reflectance as a single film, the cost of silver itself is expensive so that there is a problem in the cost. Accordingly, a reflector using an aluminum thin film with a cheap price instead of silver has been used for a lamp reflector for a backlight of a liquid crystal display as well. However, since aluminum has a lower reflectance than silver, enhancement of the reflectance of a reflector using an aluminum thin film layer has been in demand.
When a low refractive index layer and a high refractive index layer are laminated on a metal layer at an appropriate thickness, it has been known, in theory, that a reflection-increasing film is obtained. Since this reflection-increasing film can be a reflector having a higher reflectance as compared to a single body of metal, it is considered possible to respond to the aforementioned market demand. As a substrate of this reflection-increasing film, glass has been conventionally used. There has been disclosed a reflector for a laser, for example, in JP1986-185986A, JP1989-76788A or the like. However, when such glass is used as a substrate, there are problems in the processability such that a reflector cannot be bent and in the productivity such that a roll-to-roll production is not possible. In order to solve the problems, a reflection-increasing film having a polymer film as a substrate has been needed.
A reflection-increasing film using a polymer base has been disclosed, for example, in JP1999-2707A, JP2002-55213A and the like. However, an effect of increased reflectance of their reflector is relatively small so that a reflector having much higher reflectance has been in demand.